1. Field of the Invention
The present invention relates to an interface effective/ineffective state judging device and method suitably used in a computer, a printer or the like equipped with an interface such as an RS-232C (ANSI/EIA 232-D) interface.
2. Description of the Related Art
A printer widely used as an output device of a personal computer or a word processor is equipped with an RS-232C interface which is a serial interface and a Centronics interface which is a parallel interface as a host interface for data communication with a host. Either one of the two interfaces is generally selected and used by switching using software from the host or a switching operation in an operation section in the printer.
For example, when data communication is established between the host computer and the printer via the RS-232C interface, the printer and the host computer are connected to each other by a dedicated communication cable. In addition, the operation section in the printer is operated, to select the RS-232C interface.
For example, when a user forgets to connect the cable, the cable is incompletely connected, or the connection between connectors is interrupted after the cable is connected, data communication cannot be established between the host computer and the printer.
In the prior art, however, there was no means for determining whether the interface is in an effective state where data communication can be established or in an ineffective state where data communication cannot be established. Therefore, the user may, in some cases, meaninglessly wait for output by uselessly sending data from the host computer to the printer.